Project Summary: Over 81,000 new individuals are diagnosed each year with urothelial carcinoma (UC) of the bladder and 17,000 will die from their disease. Most have non-muscle invasive disease (NMIBC) at diagnosis. Despite standard treatment with the live, attenuated mycobacterial strain Bacillus Calmette-Guerin (BCG) instilled into the bladder, two-thirds of NMIBC patients will develop relapsed tumors after BCG treatment. While curative, cystectomy is associated with life-altering quality of life impact and is not feasible, or is refused, in many. Nonsurgical curative options for BCG-relapsing NMIBC patients are lacking. In metastatic UC, durable responses with low toxicity rates have been observed with checkpoint inhibitor (CPI) therapies aimed at the programmed cell death protein 1 (PD-1) / programmed death-ligand 1 (PD-L1) pathway leading to the FDA approval of five agents. Examining novel combination approaches including CPIs in BCG-relapsing NMIBC represents a natural next step. In this proposal, we plan to define the safety and clinical activity, assess the point-of-care diagnostic potential of several genomic biomarker platforms, and perform initial mechanistic investigations of novel combinations of CPI therapy with both BCG and radiation in the multi-arm, multi-stage ADAPT-BLADDER phase 1b/2 clinical trial, with the long-term goal of informing the design of future practice-changing phase 3 trials. Objectives: 1) To demonstrate safety and clinical efficacy of immunotherapy combination regimens in patients with BCG-relapsing NMIBC; 2) To identify conserved candidate genomic signatures associated with clinical benefit and/or treatment resistance to novel immunotherapy regimens in NMIBC patients with recurrent tumors after prior BCG therapy; 3) To demonstrate the existence of tumor antigen-specific T-cell responses and correlate such responses with clinical outcomes to novel immunotherapy regimens in NMIBC patients with recurrent tumors after prior BCG therapy. Methods: We will assess each objective prospectively through the multi-center phase 1 b / 2 ADAPT- BLADDER trial in over 170 patients with BCG-relapsing NMIBC. Specifically, we will document the safety of each regimen in phase 1 and clinical efficacy in phase 2. We will correlate baseline and post- treatment genomic biomarker signatures with clinical benefit. Lastly, we will interrogate the ability of personalized neoantigen peptide libraries to expand antigen-specific T-cell clones. We hypothesize that immunotherapy combination regimens will be safe and effective. Moreover, we anticipate the identification of point-of-care genomic biomarker signatures that can distinguish patients most likely to benefit; we expect to identify novel gene expression signatures predictive of therapy response and resistance; and we suspect the planned functional tumor immunology investigations will yield illuminating discoveries.